The biggest heist was pulled on celebrity jewellery dealer John Calleija, whose clients include Zara Phillips and Colin Firth

Mr Calleija then turned to put the cash counting machine away – the moment at which the real euros were allegedly switched for bundles of fake notes with “facsimile” written on them – concealed by paper bands on the outside.

The diamonds were then collected from Mr Calleija’s shop.

Prosecuting, David Hughes said: “You can imagine his horror when he goes to check the cash.